1. Field of the Invention
The present invention relates to a semiconductor photonic device comprising InxGayAl2N (group III nitride semiconductor crystal).
2. Description of the Related Art
Recently, great attention has been attracted to GaN-based thin films and ZnSe-based thin films as light emitting device materials which emit blue light as UV rays. However, the ZnSe thin films have the fatal defect that the life time is short when they are used as a light emitting device.
The InxGAyAl2N thin film is regarded as a prospective material with respect to the life time, but there is a problem in that it is difficult to grow a single crystal of InxGayAl2N having a large diameter.
In order to solve this problem, there has been proposed a so-called heteroepitaxial growth method by which a single crystal is grown on a substrate made of a material different from the single crystal is employed. In general, the single crystal is grown on a C-plane sapphire substrate.
However, the C-plane sapphire substrate has no cleavage plane perpendicular to the principal plane of the substrate. Accordingly, when an InxGayAl2N thin film is formed on the C-plane sapphire substrate, it is impossible to form a pair of resonant facets in the InxGayAl2N thin film on the C-plane sapphire substrate by a cleavage method which is often used for forming a GaAs-based semiconductor laser chip. This means that it is necessary to form the resonant facets in the InxGayAl2N thin film on the C-plane sapphire substrate by chemical etching, dry-etching, polishing or the like, which generally have a low production efficiency.
In addition, the C-plane sapphire substrate has a great hardness. This property causes a problem in that the semiconductor photonic devices formed by using the C-plane sapphire substrate are difficult to cut into respective chips of the semiconductor photonic devices. For example, it takes a considerably great time to dice the C-plane sapphire substrate on which large number of semiconductor photonic devices are formed.
The present invention can solve the aforementioned problems and provide a semiconductor photonic device comprising a substrate which is easy to cleave, thereby enabling formation of resonant cavity in a simple way and achieve chip separation easily.
The semiconductor photonic device according to the present invention includes a ZnO film formed above a substrate having a cleavage plane perpendicular to the substrate principal plane and good cleavage properties, and a semiconductor compound layer expressed by InxGayAl2N (x+y+z=1, 0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61).
In the semiconductor photonic device of the present invention, the semiconductor layer is formed on the substrate having good cleavage properties. Accordingly, the substrate can be simply cleaved with a mechanical means such as scribing or the like, without using chemical etching, and thereby a resonant face can be formed by the cleavage and chip separation can also be performed by the cleavage.
As the substrate having good cleavage properties, for example, a A-plane sapphire substrate, a (111), (100), or (110) crystal orientation M-plane sapphire substrate having a ZnS structure, a GaP substrate, a GaAs substrate and an InP substrate may be employed. These substrates are inexpensive, and therefore the substrate cost is low. Accordingly, an inexpensive light emitting device can be produced. The GaP, GaAs, and InP substrates have a low resistance, and thereby, an electrode can be formed on the back side of an optical element.
The lattice constant in the a-axial direction of the ZnO film is nearly equal to that in the a-axial direction of the InxGayAl2N. Accordingly, when the above substrates are used, a c-axially oriented ZnO film is formed, and through the ZnO film, a semiconductor compound layer made of InxGayAl2N with good crystallinity can be grown on an optional substrate.
Further, by forming a metal film on the substrate, and forming the ZnO film on the metal film, a desirably c-axially oriented ZnO film can be obtained, and the semiconductor compound layer made of InxGayAl2N with good crystallinity can be grown thereon. Further, by forming a metal film on the substrate, the metal film can be used as a lower electrode. Thus, the electrode structure of the semiconductor photonic device can be simplified.